Effect of carrier droplet size and shape at different viral loads on virus stability during environmental drying

In the aftermath of the COVID-19 pandemic, airborne transmission has been identified as a significant factor in disease spread. However, there have been very few direct comparisons of virus viability in airborne droplets versus those deposited on surfaces or fomites. This study compares the viability of the enveloped Phi6 virus and two non-enveloped viruses (T4 and MS2) in droplets on hydrophobic and hydrophilic surfaces at 25°C and 45%–55% relative humidity. The former results in spherical droplets similar to airborne droplets, while the latter pertains to spreading droplets comparable to a fomite state. Our research highlights the influence of various physical factors of the carrier droplet—such as its shape and size—as well as the type and concentration of the virus on its viability during the drying process. We found that, at a fixed volume, virus viability decreased with droplet size in spherical droplets, while high initial viral concentrations (~ 10^5 pfu/μL) improved survival on fomites. This suggests that fomites from individuals with high viral loads pose a greater risk of infection. Overall, droplets of a specific volume are more viable in the air than on surfaces. Smaller airborne droplets may have decreased viability but can linger longer and penetrate deeper into the respiratory tract. When viral loads are high, its comparable persistence in both spherical and flat droplets increases the risk of fomite transmission.